Is keeping a device at 100% battery through continuous charging better than repeated discarding?

Note: I just I meant to say discharging in the title.

I have a new android tablet. I also have a charger with a long cord that allows me to keep it plugged in comfortably a vast majority of the time. What’s worse for battery longevity, keeping it plugged in at 100%, or allowing it to significantly discharge and recharging it regularly? Assume modern lithium ion technology.

It’s my understanding that Li-ion batteries (which a newer tablet likely has) don’t suffer from any type of memory like the older Ni-Cads did. That is, they don’t need to be discharged to near zero, then charged up to 100%.

Having said that, if you’re going to keep it plugged in nearly all the time, it’s not really going to be a concern. My laptop gets unplugged a small handful of times in the rare circumstances that I need to use it in another room (read a recipe, plug it directing into the router etc). Given that, I really don’t care if the battery only lasts 1 or 2 hours instead of 5 or 6.

Something makes me think that the life of a Li-Ion battery is cycle dependet. That is they get X amount of discharges and recharges before the quality drops off. However, those are full cycles., so if it drops to 95% and you charge it back up, that’s only 5% of a cycle. But I could be wrong about that part.

Having said that, even if the battery life totally falls apart, it’ll still work (or should still work) if it’s plugged in. Furthermore, by the time you have battery issues, regardless of how long it takes you’ll probably be in the market for a new one anyway. And, if not, uBreakiFix can likely replace the battery for you (assuming it’s not user serviceable) and you’ll be able to get another few years out of it.

The correct answer is none of the above. Both keeping a lithium ion battery at 100 percent and deep discharging it over and over will cause the battery to wear out faster. If you are going to keep the device plugged in all the time, it is best to keep the charge level down at about 80 percent.

Many laptops and other mobile devices have a charging mode under their settings so that they will do this automatically. On laptops it is typically called long lifespan mode or something similar. I haven’t searched for the setting on my tablet so I don’t know what it is typically referred to on Android.

Another important factor is that time takes its toll on Lithium batteries, regardless of how carefully you treat them - they just lose a portion of their capacity as a function of age.


I know that the Tesla Model S (and probably their other cars) by default will not charge to the full rated capacity of the battery; this extends the useful lifetime of the battery for most users. If you want to charge to full rated capacity (because you want to take a long road trip without stopping in the middle to charge), then you have to go into the menus (before charging) and select “max range mode” or something like that.

JoeyP is correct in saying that the newest in batteries don’t have an overcharge problem. Our Chromebooks have Lithium Ion batteries and they are made to stop accepting a charge when they reach 100%, so unplugging them isn’t necessary. Having said that, I must add that reading the specs for your specific device and heading all directions is highly recommended. ASSuming always creates an element of chance. LOL

IIRC all EVs and hybrids do this.

It is very bad for a LiIon battery to be kept on a continuous charging current when full (this is a sharp difference from older technologies).

However, this is not necessarily the same as keeping the device plugged in.

Both my 4-year-old Android phone and my 4-year-old laptop will cut off charging when the battery reaches 100%.

I can tell both by looking at battery voltage (*#0228# on my phone) and by the fact that the battery level will actually go down below 100% after a while even when I keep the device plugged in.

If you make sure your device does this, then you could be much less concerned about leaving it plugged in all the time.

So look for the long lifespan setting or try to find out if the device does it automatically.